This invention relates to a device for measuring alternating current flowing in an electric conductor such as, for example, an insulated a.c. mains wire.
It is an object of the invention to provide such a device which may be constructed at low cost, which has no moving parts, and which may be made with high precision.
According to the present invention there is provided a device for measuring alternating current in a conductor, the device comprising a first set of coils each comprising at least one conductive track deposited on an electrically insulating body, and an electrically insulating coil support member, wherein said coils are mounted on the support member along a path defining a notional loop and are connected in series by a conductive track deposited on the support member, the support member being configured to allow a conductor to be introduced into the into the interior of the notional loop with the axis of the conductor normal to the plane containing the coils, the device further including means for deriving the alternating current in the conductor as a function of the voltages induced in the series-connected coils.
In a preferred embodiment there are an even number 2N of substantially identical coils, with a first set N of the coils mounted on the support member substantially equally spaced around a first notional circle and connected in series by a first conductive track deposited on the support member, and a second set N of the coils mounted on the support member substantially equally spaced around a second notional circle and connected in series by a second conductive track deposited on the support member, the second circle being substantially concentric with the first circle, the support member being configured to allow a conductor to be introduced into the centre of the concentric circles with the axis of the conductor normal to the plane containing the coils, and the device further including means for deriving the alternating current in the conductor as a function of the voltages induced in the first and second sets of series-connected coils.